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2009: Vorlesungen und Vorträge des Physikalischen Instituts


2009: Vorlesungen und Vorträge des Physikalischen Instituts

Das Physikalische Institut lädt im Rahmen seines Physikalischen Kolloquiums jedes Semester nationale und internationale Wissenschaftlerinnen und Wissenschaftler ein, um Ihr jeweiliges Forschungsgebiet vorzustellen.

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  1. Ex(e/o)rcising Demons: Brownian Motors at Work on the Nanoscale

    Peter Hänggi (Institut für Physik, Univ. Augsburg)

    19.1.2009: Prof. Dr. Peter Hänggi (Institut für Physik, Univ. Augsburg): Noise is usually thought of as the enemy of order rather than of a constructive influence. For the phenomena of Brownian motors, however, noise can play a beneficial role in enhancing and facilitating directed transport in absence of biasing forces. We identify variety of intriguing beneficial applications in physical, technological, and biomedical contexts. In their modus operandi such classical and quantum Brownian motors use the energy from the haphazard source of thermal noise in order to perform work against external loads. The basic principles that underpin directed transport in quantum optical and solid-state based devices are elucidated for various nonlinear systems. The very presence of non-equilibrium disturbances enables a Brownian motor to overcome the limiting laws imposed by thermal equilibrium, thereby rectifying quantum Brownian motion for shuttling efficiently quantum objects along a priori designed routes.

  2. From quantum search to light harvesting - Dynamics in complex systems

    Oliver Mülken (Physikalisches Institut, Univ. Freiburg)

    26.1.2009: Dr. Oliver Mülken (Physikalisches Institut, Univ. Freiburg): In diesem Vortrag soll der Bogen zwischen unterschiedlichsten physikalischen Prozessen geschlagen werden. Ein Extrem sind quantenmechanische Suchalgorithmen, wie sie u.U. für Quantencomputer verwandt werden können. Auf der anderen Seite steht der hocheffiziente Energietransport bei der Photosynthese, bei dem momentan debattiert wird, in wie weit kohärente Dynamik verantwortlich für die hohe Effizienz ist. Beide Prozesse lassen sich mit Hilfe von Netzwerken und ähnlichen Modellen für die Dynamik von Anregungen (bspw. Ladung oder Energie) beschreiben. Die Verbindung zwischen beiden Extremen soll anhand von Beispielen verdeutlicht werden. Hierzu wird der Transport mit langreichweitigen Dipol-Dipol Wechselwirkungen und der Effekt der Absorption von Anregungen behandelt.

  3. Physik für Mediziner und Pharmazeuten (WS 2008/2009)

    Ulrich Landgraf

    Prof. Dr. Ulrich Landgraf: Vorlesung vom 24. November 2008

  4. Wave propagation in random media: diffusion vs. localization

    Thomas Wellens (Physikalisches Institut, Univ. Freiburg)

    16.2.2009: Dr. Thomas Wellens (Physikalisches Institut, Univ. Freiburg): As it is well known, waves are fundamentally distinct from (classical) particles in their ability to display interference. However, in presence of disorder, interferences tend to be washed out. In this case, wave propagation reduces to a simple diffusion process - like a random walk of a classical particle ("soccer ball in the forest"). But under appropriate circumstances, some interferences may also survive the disorder average and induce interesting effects, for example turn a metal into an insulator (Anderson localization) or increase the brightness of saturn's rings (coherent backscattering). After a general introduction into the physics of multiple scattering, the second part of the talk deals with propagation of waves in nonlinear random media. Generally, a nonlinearity arises whenever the wave interacts with itself or with the scattering medium in such a way that properties like refractive index, mean free path, etc., are not constant, but depend on the wave intensity. The question is now: how do these nonlinearities affect the multiple scattering interferences? To tackle this problem, I will develop a diagrammatic theory for performing disorder averages with nonlinear wave equations. As main result, I show how the coherent backscattering interference is either diminished or amplified, depending on the type of nonlinearity.

  5. Can relativity be considered complete?

    Nicolas Gisin (Group of Applied Physics, University of Geneva)

    15.4.2009: Prof. Dr. Nicolas Gisin (Group of Applied Physics, University of Geneva): Großer Hörsaal der Physik

  6. Quantum physics in in quantum dots

    Klaus Ensslin (ETH-Zürich)

    27.4.2009: Prof. Dr. Klaus Ensslin (ETH-Zürich): Electrons in quantum dots are confined in all three spatial dimensions. In semiconduc-tors the confinement potential, the number of the electrons and the tunnel coupling of the quantum dot to the outside world can be tuned by gate electrodes. With suitable detec-tors it is possible to monitor the current through the quantum dot in a time-resolved fash-ion on the level of individual electrons allowing ultra-sensitive current and noise meas-urement. Similar to a double slit experiment in vacuum, the Aharonov-Bohm effect can be exploited in a ring geometry to measure the interference of individual electrons. For coupled quantum systems the question of back action and correlated detection can be investigated. While this development has lead to exquisite control of quantum systems in conventional semiconductors, quantum dots in graphene, a single layer of carbon atoms, hold the promise for ever smaller and better controlled quantum structures and longer coherence times.

  7. Carbon Nanotechnology: From Beer Storage to Ultrafast Lasers

    Andrea C. Ferrari (University of Cambridge)

    11.5.2009: Prof. Dr. Andrea C. Ferrari (University of Cambridge): Carbon based materials play a major role in tod ay's science and technology. Carbon is a very versatile element, which can crystallise in the form of diamond or graphite. Great excitement has followed the discovery of new forms of carbon, including the spherical shaped fullerenes, the one-dimensional nanotubes and the two dimensional graphene (a single layer of graphite). There are also many non-crystalline carbons, known as amorphous and nanostructured carbons (mixture of amorphous and graphitic carbon, nanotubes and fullerenes). Diamond-like carbons play an important role, being a key element in numerous everyday-life applications. Their great versatility arises from the strong dependence of the physical properties on the ratio of sp2 (graphite-like) to sp3 (diamondlike) bonds. Here I will review the main properties of diamond-like carbon, nanotubes and graphene, discussing a variety of applications for these materials, ranging from data or beer storage, to ultrafast optoelectronics.

  8. The Coming Revolutions in Particle Physics

    Chris Quigg (Theoretical Physics Department Fermi National Accelerator Laboratory)

    26.10.2009: Dr. Chris Quigg (Theoretical Physics Department Fermi National Accelerator Laboratory)

  9. Observation, dynamics and control of Quantum Entanglement

    Florian Mintert (Universität Freiburg)

    2.11.2009: Dr. Florian Mintert (Universität Freiburg)

  10. Quantenmechanische und klassische Beschreibung der Dynamik von Biomolekülen

    Gerhard Stock (Universität Freiburg)

    16.11.2009: Prof. Dr. Gerhard Stock (Universität Freiburg)

  11. Dynamics of recurrent pulse-coupled networks in the brain

    Stefan Rotter (Universität Freiburg, Bernstein Center for Computational Neuroscience Freiburg)

    30.11.2009: Prof. Dr. Stefan Rotter (Universität Freiburg, Bernstein Center for Computational Neuroscience Freiburg)

  12. Photoeffect in Molecules, Old Questions – New Answers

    Reinhard Dörner (Universität Frankfurt)

    07.12.2009: Prof. Dr. Reinhard Dörner (Universität Frankfurt)

  13. Theorie der elektroschwachen Wechselwirkung - Status und Perspektiven

    Stefan Dittmaier (Universität Freiburg)

    21.12.2009: Prof. Dr. Stefan Dittmaier (Universität Freiburg)

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